Radio Frequency Plasma Power Research Articles

Combined ns pulsed-RF excitation and impedance matching considerations for the production of moderate E/n atmospheric pressure discharges for gas conversion

Sub-breakdown radiofrequency (RF) discharges enabled by a nanosecond (ns) pulse ignition source are studied at atmospheric pressure in a range of gas mixtures from completely inert (in Ar) to completely reactive (in CO2). An electrical characterisation of the continuous wave (CW) RF discharge (13.56 MHz) is performed to determine plasma impedance and plasma power dissipation. Two different measurement methods to electrically characterize the system are described and compared. One method uses in-situ measurements of discharge parameters (voltage, current and the phase angle), and the other method performs ex-situ measurements of the load circuit using a vector network analyser. It was found that RF plasma power deposition depended on the applied RF power as well as the gas mixture composition. Using the in-situ voltage, current and phase angle measurements, plasma power deposition was calculated to be as much as 85% and 76% of the applied RF power for the pure Ar and pure CO2 cases, respectively. A preliminary qualitative assessment of the plasma composition was performed by optical emission spectroscopy, and CO2 conversion by mass spectrometry. CO2 to CO conversions of 11.2% and 5.5% in a 20:80 (CO2:Ar) mixture and in 100% CO2, respectively, were observed. This study demonstrates a RF plasma source for gas conversion applications at atmospheric pressure in a completely reactive gas.

An analysis and preliminary experiment of the discharge characteristics of RF ion source with electromagnetic shielding

Combined with two-dimensional (2D) and three-dimensional (3D) finite element analysis and preliminary experimental tests, the effects of size and placement of the electromagnetic shield of the radio-frequency (RF) ion source with two drivers on plasma parameters and RF power transfer efficiency are analyzed. It is found that the same input direction of the current is better for the RF ion source with multiple drivers. The electromagnetic shield (EMS) should be placed symmetrically around the drivers, which is beneficial for the plasma to distribute uniformly and symmetrically in both drivers. Furthermore, the bigger the EMS shield radius is the better generating a higher electron density. These results will be of guiding significance to the design of electromagnetic shielding for RF ion sources with a multi-driver.

Impact of Radio Frequency Plasma Power on the Structure, Crystallinity, Dislocation Density, and the Energy Band Gap of ZnO Nanostructure

The aim of this study is to investigate the effect of radio frequency (RF) plasma power on the morphology, crystal structure, elemental chemical composition, and optical properties of ZnO nanostructure using a direct current magnetron sputtering technique. This study emphasized that the growth rate and surface morphology of the polycrystalline ZnO were enhanced as the radio frequency (RF) plasma power increased. This can be observed by fixing other parameters such as the growth time, substrate temperature, and chamber partial pressure. The RF plasma power alteration from 150 to 300 W can produce uniform nanograin, spheroid, and nanorods. Additionally, the RF plasma power alteration leads to the alteration in the ZnO nanorod diameter from 14 to 202 nm. It was observed that the XRD intensities are increased at higher plasma powers. This, perhaps, can be inferred from the transformation of the granular microcrystals to the needlelike or platelike large crystals, as already examined using SEM images. This also has an impact on the average crystalline size, which increased from 10 to 40 nm on increasing the RF plasma power. Moreover, the increase of the RF plasma power has an obvious impact upon the optical band-gap energy, which was accordingly decreased from 3.26 to 3.22 eV. Finally, the absorption band edge was shifted to a lower-energy region due to the quantum size effect at the nanorange.

Direct growth of graphene films without catalyst on flexible glass substrates by PECVD* *Project supported by the National Natural Science Foundation of China (Grant No. 51302215), the Joint Research Funds of Department of Science & Technology of Shaanxi Province and Northwestern Polytechnical University, China (Grant No. 2020GXLH-Z-029), and the Natural Science Basic Research Program of Shaanxi Province, China (Grant Nos.

A hydrogen-plasma-etching-based plasma-enhanced chemical vapor deposition (PECVD) synthesis route without metal catalyst for preparing the graphene films on flexible glass is developed. The quality of the prepared graphene films is evaluated by scanning electron microscopy, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, ultraviolet-visible spectroscopy, and electrochemical measurements. In a radio frequency (RF) power range of 50 W–300 W, the graphene growth rate increases with RF power increasing, while the intensity ratio of D- to G-Raman peak (I D/I G) decreases. When the RF power is higher than 300 W, the I D/I G rises again. By optimizing experimental parameters of hydrogen plasma etching and RF power, the properties of as-prepared flexible graphene on glass are modulated to be able to achieve the graphene’s transparency, good electrical conductivity, and better macroscopic uniformity. Direct growth of graphene film without any metal catalyst on flexible glass can be a promising candidate for applications in flexible transparent optoelectronics.

Optimization of instrumental parameters for improving sensitivity of single particle inductively-coupled plasma mass spectrometry analysis of gold

Single particle inductively-coupled plasma mass spectrometry (spICP-MS) is a promising technique for analysis of engineered nanoparticles, whose utilization has increased substantially over the past years. Optimization of instrumental conditions is, however, crucial to improve the sensitivity and precision of nanoparticle (NP) detection. In this study, the influence of ICP-MS instrumental parameters (nebulizer gas flow, plasma radiofrequency-power and sampling depth) on the signal intensity of gold in spICP-MS was evaluated using dispersions of Au NPs and a solution of dissolved gold. The interaction effects of the main factors were found to have a significant effect on the signal intensity, proving that factor values should be jointly optimized instead of one at a time, if maximum ion signal is expected. Optimization of instrumental parameter values was performed for both analyte forms and found to be in a good agreement, indicating a similar behavior of the particles in plasma compared with the dissolved analyte. However, some differences in the behavior of the two analyte forms as regard to sampling depth position was observed. Particle size or the presence of complex sample matrix was not found to influence the optimal instrumental parameter values, however, a significant signal depression for gold was observed (up to 50%) in matrices containing high levels of sodium. Compared to frequently used ‘robust conditions’, a 70% increase in the ion signal intensity of gold and a 15% decrease in the particle size detection limit was achieved with instrumental parameter optimization. As such, instrumental parameter optimization for sensitive NP analysis can be seen as highly beneficial procedure.

Combined effects of oxygen pressures and RF powers on the electrical characteristics of ITO-based multilayer transparent electrodes

The opto-electrical properties of plasma-treated ITO films were investigated as functions of oxygen pressures (3.33 and 26.66 Pa) and radio-frequency (RF) plasma powers (50 and 150 W). The plasma-treated samples showed higher transmittance than the untreated sample. After the low-oxygen treatment, the carrier concentration increased with increasing plasma RF power and the figure of merit (FOM) also increased from 1.17 × 10−3 to 1.65 × 10−3 Ω−1. This was not the case for the high-oxygen treatment. The ITO surfaces became smoother with increasing RF power. It was shown that unlike the high-oxygen treated samples, the In 3d and Sn 3d core levels for the low-oxygen-treated ITO films were shifted to higher energies compared to that of the untreated sample. ITO films of ITO/Ag/ITO multilayers (IAI) were plasma-treated at different conditions. Their transmittance maxima were in the range of 91.58–92.32% at 492–501 nm. The bottom-ITO-treated sample gave 23.1% higher mobility and 19% lower sheet resistance than the untreated IAI. The wetting characteristics of deionized (DI) water on the ITO films showed that the surface energy of ITO films increased from 34.22 to 71.14 mJ/m2 when the oxygen pressures increased from 0 to 26.66 Pa.

Observation and mitigation of RF-plasma-induced damage to III-nitrides grown by molecular beam epitaxy

In this work, radio-frequency (RF) plasma-induced damage to III-nitride surfaces and bulk defects is observed and mitigated. It is shown that for InN films, the surface is more sensitive to plasma-induced damage than GaN films, as observed via atomic force microscopy and reflection high energy electron diffraction. In order to isolate any possible plasma-induced damage, a growth window for InN is established, and temperature ranges are determined for other damaging effects which include roughening due to low adatom mobility, InN decomposition, and indium desorption. In situ plasma monitoring and optimization are accomplished with a combination of optical emission spectroscopy as well as a remote Langmuir probe. It is shown that by increasing the plasma nitrogen flow, the positive ion content increases; however, the ion acceleration potential reduces. Additionally, a reduced RF plasma power results in a reduction of atomic nitrogen species. These plasma species and energetic variations result in variations in the bulk unintentional background electron concentrations observed by room temperature Hall effect measurements of ∼1 μm thick InN films. By increasing the nitrogen flow from 2.5 to 7.5 sccm for a constant RF power of 350 W, the background electron concentration decreases by 74% from 1.36 × 1019 cm−3 to 3.54 × 1018 cm−3, while maintaining a smooth surface morphology. Additionally, photoluminescence spectra indicate optical emission energies shift from ∼0.81 to 0.71 eV (closer to the fundamental bandgap of InN) by limiting the damaging plasma species. Finally, conditions are presented to further minimize plasma-induced damage in III-nitride devices.

Characterization of particle generated during plasma-enhanced chemical vapor deposition on amorphous carbon layer using particle beam mass spectrometer

Nanoscale particles that can affect the process yield were generated using the plasma-enhanced chemical vapor deposition (PECVD) process. A particle beam mass spectrometer is remarkably useful to understand particle behavior in a reactor. The properties of nanoscale particles obtained from the exhaust line of PECVD during amorphous carbon layer (ACL) growth under various growth conditions were investigated. The number concentration and the size of the nanoscale particles generated were quite sensitive to growth parameters such as radio frequency (RF) plasma power, C2H2, and dopant (i.e., NH3 and B2H6) gas flow rate. For an ACL growth at higher RF plasma power, the average size of the nanoscale particles decreased as the number concentration of particles increased while they are opposingly increased in particle size and decreased in concentration for a higher C2H2 flow rate. A reduction in both the average nanoscale particle size and their number concentration occurred when NH3 gas was used for nitrogen-doped ACL. By contrast, ACL growth with increasing B2H6 gas flow for boron-doped ACL exhibited a larger average nanoscale particle size and number concentration. The particle number concentration was in the range of 106–108 cm−3 with average particle sizes of 100–400 nm. According to this study, the measurement of real-time particle size distribution can help to minimize the number of generated particles and optimize the ACL deposition process.

Catalytically solid-phase self-organization of nanoporous SnS with optical depolarizability

The catalytic solid-phase synthesis of self-organized nanoporous tin sulfide (SnS) with enhanced absorption, manipulative transmittance and depolarization features is demonstrated. Using an ultralow radio-frequency (RF) sputtering power, the variation of the orientation angle between the anodized aluminum oxide (AAO) membrane and the axis of the sputtered ion beam detunes the catalytically synthesized SnS from nanorod to nanoporous morphology, along the sidewall of the AAO membrane. The ultraslow catalytic sputtering synthesis on the AAO at the RF plasma power of 20 W and the orientation angle of 0° regulates the porosity and integrality of nanoporous SnS, with average pore diameter of 80-150 nm. When transferring from planar to nanoporous structure, the phase composition changes from SnS to SnS2-Sn2S3, and the optical bandgap shrinks from 1.43 to 1.16 eV, due to the preferred crystalline orientation, which also contributes to an ultralow reflectance of <1% at 200-500 nm when both the transmittance and the surface scattering remain at their maxima. The absorption coefficient is enhanced by nearly one order of magnitude with its minimum of >5 × 10(4) cm(-1) at the wavelength between 200 and 700 nm, due to the red-shifting of the absorption spectrum to at least 100 nm. The catalytically self-organized nanoporous SnS causes strong haze and beam divergence of 20°-30° by depolarized nonlinear scattering at the surface, which favors the solar energy conversion with reduced surface reflection and enhanced photon scattering under preserved transmittance.

Control of carbon content in amorphous GeTe films deposited by plasma enhanced chemical vapor deposition (PE-MOCVD) for phase-change random access memory applications

Amorphous and smooth GeTe thin films are deposited on 200 mm silicon substrates by plasma enhanced—metal organic chemical vapor deposition (PE–MOCVD) using the commercial organometallic precursors TDMAGe and DIPTe as Ge and Te precursors, respectively. X-ray photoelectron spectroscopy (XPS) measurements show a stoichiometric composition of the deposited GeTe films but with high carbon contamination. Using information collected by Optical Emission Spectroscopy (OES) and XPS, the origin of carbon contamination is determined and the dissociation mechanisms of Ge and Te precursors in H2 + Ar plasma are proposed. As a result, carbon level is properly controlled by varying operating parameters such as plasma radio frequency power, pressure and H2 rate. Finally, GeTe films with carbon level as low as 5 at. % are obtained.

The effect of oxygen flow rate and radio frequency plasma power on cubic ZnMgO ultraviolet sensors grown by plasma-enhanced molecular beam epitaxy

Cubic Zn1−xMgxO thin films were produced by Plasma-Enhanced Molecular Beam Epitaxy. Oxygen flow rate and applied Radio-Frequency (RF) plasma power were varied to investigate the impact on film growth and optoelectronic device performance. Solar-blind and visible-blind detectors were fabricated with metal-semiconductor-metal interdigitated Ni/Mg/Au contacts and responsivity is compared under different growth conditions. Increasing oxygen flow rate and RF plasma power increased Zn incorporation in the film, which leads to phase segregation at relatively high Zn/Mg ratio. Responsivity as high as 61 A/W was measured in phase-segregated ZnMgO visible-blind detectors.

Zinc oxide (ZnO) grown on flexible substrate using dual-plasma-enhanced metalorganic vapor deposition (DPEMOCVD)

This study investigates the temperature dependence of zinc oxide (ZnO) grown on polyestersulfone (PES) flexible substrates using the dual plasma-enhanced metal–organic chemical vapor deposition (DPEMOCVD) system. The proposed method uses a direct voltage (DC) and radio-frequency (RF) plasma system. The group-VI precursor, oxygen (O2), can be completely ionized by the DC plasma system. The effect of optimal DC plasma power on ZnO thin films is thoroughly investigated using X-ray diffraction (XRD). The experimental results indicate that the crystalline structure and optical and electrical properties of ZnO thin films grown on PES substrates are dependent on the deposition temperature. The optimum deposition temperature for ZnO thin films deposited on PES substrates is 185°C, whereas the DC and RF plasma power is 1.8W and 350W, respectively. Additionally, the wettability characteristic regarding the UV irradiation time was assessed by measuring the water contact angle. Under the UV irradiation for 60min, the ZnO film grown at 185°C represents a low contact angle of 5°, which approaches to a superhydrophilic surface.

Challenges in Self-Consistent Full-Wave Simulations of Lower Hybrid Waves

Analysis of wave propagation in the lower hybrid range of frequencies (LHRF) in the past was done using ray tracing and the Wentzel-Kramers-Brillouin approximation taking advantage of the very small scale of those waves. To include the effects of wave diffraction and focusing in this regime, full-wave simulation is necessary but requires significantly more computational power. In both ray tracing and full-wave simulations in the LHRF, it is also essential to include the self-consistent evolution of the electron distribution in response to the waves. This adds a considerable computational burden in constructing the stiffness matrix for the system [Valeo , “Full-wave Simulations of LH wave propagation in toroidal plasma with non-Maxwellian electron distributions,” 18th Topical Conference on Radio Frequency Power in Plasmas, AIP Conference Proceedings (2007)]. Advances in algorithms and the availability of massively parallel computer architectures have permitted the solving of the Maxwell-Vlasov system for wave propagation directly [Wright , Phys. Plasmas (2009), 16, July]. We will discuss the various modeling advances that have led to this capability, including various memory-management approaches, physics-motivated algorithm adaptions appropriate to the LHRF, and improvements in the matrix solver to minimize communication overhead when using thousands of cores on leadership-class computer platforms. Of particular importance have been the use of verification and validation techniques and the analytic approximations to the imaginary (pole residue) contribution to the plasma dielectric response.

Inactivation Characteristics of Bacteria in Capacitively Coupled Argon Plasma

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Plasma technology is being focused on the medical, food, and pharmaceutical fields for sterilization applications. The sterilizing effect of the 13.56-MHz radio-frequency (RF) plasma generated by using argon gas was studied using <emphasis emphasistype="boldital">Staphylococcus aureus</emphasis>, one of the most common pathogens liable to hospital-acquired infections. The major focus of this paper was to perform a parametric study by varying the external-process parameters such as plasma treatment time, RF power, gas-flow rate, and pressure on the inactivation of <emphasis emphasistype="boldital">S. aureus</emphasis>. The results were supported by optical emission spectroscopy and scanning electron microscopy studies. </para>

Effects of gas pressure and plasma power on the growth of carbon nanostructures

Effects of gas pressure and plasma power on the growth of carbon-based nanostructures (CNSs) have been studied in detail. Multi-walled carbon nanotube (MWCNTs) and carbon nanowalls (CNWs) were synthesized on glass substrates via radio frequency plasma-enhanced chemical vapor deposition (RFPECVD) technique. Surface morphologies of the films have been studied by SEM and TEM. When the gas pressure increases from 120 to 300 Pa, the deposited carbon material changes from MWCNTs to carbon nanowalls (CNWs). Additionally, the density of carbon nanostructures increases with the gas pressure. The radio frequency (RF) plasma power ranging from 600 to 2400 W was applied during the activation and deposition process. The plasma enhances the decomposition of carbon atoms to deposit onto the surfaces of catalyst particles. Whereas an exorbitant RF plasma power can destroy the already deposited carbon nanostructures.

The structural ordering of thin silicon films at the amorphous to nano-crystalline phase transition by GISAXS and Raman spectroscopy

Thin silicon films were deposited by the plasma-enhanced chemical vapour deposition method using microwave (MW) and standard radio frequency (RF) gas discharge in silane gas diluted by hydrogen in the range that produces a mixture of amorphous and crystalline phases. The samples were analysed by Raman spectroscopy and grazing incidence small-angle X-ray scattering (GISAXS), while the threshold for the transition between the amorphous and crystalline phase was checked by the change in electrical conductivity. The crystalline fraction, estimated by Raman spectroscopy, varied between 0% and 70% while the individual crystal sizes were between 3 and 9 nm. However, the size distribution was broad suggesting also the existence of smaller and larger crystals. The “particles” observed by GISAXS, most probably voids, were in the range between 2 and 12 nm. The voids in samples deposited by MW plasma were larger when closer to the surface. Their shape indicated the formation of a columnar structure perpendicular to the surface, more pronounced at higher temperature. The samples deposited by RF plasma and low power had spherically symmetric “particles” with uniform size across the depth of the samples. An increase of the RF power resulted in the formation of a columnar structure parallel to the surface. The observed differences are discussed in relation to the difference in growing kinetics of the used deposition methods.

Simultaneous determination of Ca, P, Mg, K and Na in biodiesel by axial view inductively coupled plasma optical emission spectrometry with internal standardization after multivariate optimization

A simple and rapid method for the simultaneous determination of Ca, P, Mg, K and Na in biodiesel by axial view inductively coupled plasma optical emission spectrometry by simply diluting the sample in ethanol and using Y as internal standard is proposed. The sample (≈2.5 g) is diluted by making up the volume to 25 mL with ethanol, after the addition of 2 μg mL−1 Y(III). The plasma radiofrequency power, oxygen flow rate, the auxiliary gas flow and nebulizer pressure were optimized by factorial analysis. An oxygen flow was used to decrease the background. The obtained detection limits, in μg g−1, considering 2.5 g of sample in a final volume of 25 mL, were: 0.03 for Ca, 0.5 for P, 0.005 for Mg, 0.3 for K and 0.1 for Na. Samples of biodiesel produced from different raw materials, such as soybean oil, castor oil, cotton and animal fat, were analyzed and spiked with 5 μg g−1 of the analytes. Calibration was carried out with standard solutions in ethanol, allowing the use of stock aqueous standard solutions. All recoveries were in the range from 82 to 114% for all analytes, demonstrating the accuracy of the proposed procedure. Most of the obtained concentrations of the analytes, with RSD lower than 9%, were in the μg g−1 level.

Activated reactive evaporation deposited silicon nitride as a masking material for MEMS fabrication

Silicon nitride films were deposited in a nitrogen gas plasma by an ‘activated reactive evaporation’ (ARE) process on silicon substrates maintained at room temperature. Silicon powder was evaporated by e-beam evaporation in the presence of the nitrogen gas plasma excited by a radio frequency (RF) power source (13.56 MHz). The films deposited at 80 W RF plasma power for 30 min deposition time were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy and ellipsometry techniques. The x-ray diffraction pattern reveals the polycrystalline nature of the films with characteristics of hexagonal structure even at room temperature. X-ray photoelectron spectroscopy showed formation of silicon-rich silicon nitride. The FTIR spectrum shows Si–N bond formation and absence of Si–H bond, indicating hydrogen-free films. Scanning electron microscope shows pinhole and crack-free surface of the films without any particulates of silicon on the surface. The refractive index (η) and the thickness (d) are observed to be 1.99 and 1800 Å, respectively. The present work also describes the results on application of ‘ARE’ silicon nitride thin films as a masking material for the anisotropic etching of silicon in aqueous KOH solution. A pattern was lithographically transferred through the masking material on the silicon substrate. The etch rate of the films ∼4 Å min−1 was calculated from the masking time data of the films. The activation energy of 0.52 eV was determined by the relationship between temperature and the rate constant, which is in good agreement with the results reported in the literature. The etch rate value is low as compared to the etch rate of the conventional masking materials (60 Å min−1 for SiO2 and 8 Å min−1 for LPCVD Si3N4). Thus, ‘ARE’ silicon nitride films withstand higher concentrations of KOH for larger time periods compared to the conventional masking materials and act as a good masking material for MEMS.

Characterization of ‘ARE’ deposited silicon nitride films and their feasibility as antireflection coating

Silicon nitride films are deposited in presence of nitrogen gas plasma by ‘Activated Reactive Evaporation (ARE)’ process on silicon substrates maintained at room temperature. Silicon powder was evaporated by e-beam evaporation in the presence of nitrogen gas plasma excited by a radio frequency (RF) power source (13.56 MHz). Depositions were carried out at different RF plasma powers. The deposited films were characterized by X-ray diffraction, X-ray photoelectron and UV–Visible spectroscopy, scanning electron microscopy and ellipsometry techniques. The X-ray diffraction pattern reveals the polycrystalline nature of the films with characteristics of hexagonal structure. X-ray photoelectron spectroscopy showed formation of silicon-rich silicon nitride. Observation of the films under scanning electron microscope shows a smooth and pinhole-free surface. The film deposited at 70 W RF plasma power for 18-min deposition time showed the refractive index (‘ η’ at λ = 632.8 nm) and the thickness ( d) 1.98 and 68.5 nm, respectively. The minimum reflectivity R = 1.74% is obtained from UV–Visible spectroscopy at λ = 547 nm. For the condition of near quarter wavelength single layer antireflection coating the optical thickness of the layer was taken as a quarter wavelength d = λ/4 η at the minimum reflectivity observed for the film. The above results show the feasibility of using ‘ARE’ silicon nitride as antireflection coating.

Evaluation of slurry preparation procedures for the determination of mercury by axial view inductively coupled plasma optical emission spectrometry using on-line cold vapor generation

Five different slurry preparation procedures were tested, after grinding the solid samples to a particle size ≤53 μm: (1) using aqua regia plus HF, 30 min of sonication, standing time of 24 h followed by another 30 min of sonication; (2) same as the previous one, except that the standing time and the second ultrasound treatment were omitted; (3) same as the previous one, except that HF was not used; (4) same as the previous one, except that the aqua regia was replaced by nitric acid; (5) same as the previous one, except that the acid nitric was replaced by tetramethylammonium hydroxide (TMAH). The Hg vapor was generated on-line, and the emission signal intensity measured at 253.652 nm by axial view inductively coupled plasma optical emission spectrometry. Initially, four experimental conditions were optimized using a multivariate factorial analysis: the concentrations of HCl and of the reducing agent, NaBH 4, used in the cold vapor generation, and two instrumental parameters, the plasma radiofrequency power and the carrier gas flow rate. The radiofrequency power was statistically significant, but limited to 1.2 kW for practical reasons. The procedures were applied to 11 biological and environmental materials. Both, the slurries and the filtrates were analyzed, using calibration solutions in the same medium as in the slurries. The first three procedures produced results in agreement with the certified values. The two last procedures, using nitric acid or TMHA could not be used for quantitative analysis. For practical reasons, Procedure 3, with a detection limit (3s, n=10) of 0.06 μg g −1 for a sample mass of 20 mg in a final volume of 15 mL is recommended. The relative standard deviations for mercury in the investigated materials, using the recommended procedure, were lower than 12.5%, indicating a good precision for slurry sampling. The recommended procedure is simple, rapid and robust.